Intraocular lenses are used as artificial lens implants in eyes from which the natural lens has been removed. A natural lens changes its focal length by deformation, known as accommodation, to provide a focused image. An IOL does not focus in this manner. Monofocal IOLs provide focused vision at only a single distance range. If the focal length is selected to provide a sharp image for a distant object, then an object which is closer, for example at reading distance, will not be sharply focused on the retina. It is possible to sharply image closer objects by selecting a different focal length, but then distant objects would appear out of focus.
Bifocal IOLs are advantageous for providing clear vision at two distance ranges. U.S. Pat. No. 5,192,318, issued Mar. 9, 1993, the disclosure of which is incorporated by reference, concerns various bifocal IOL constructions. A bifocal IOL produces two superimposed images with one image always out of focus. Not all people can select between the two images and process the focused image sufficiently to see. Prior to surgery to implant a bifocal IOL in a patient, it is desirable to assure that the patient is a good candidate for a bifocal IOL. Implantation surgery carries inherent risks to the health of the patient, as with any surgery. Additional eye surgery can also damage the eye and compromise the quality of vision after surgery. Removal of an unsatisfactory lens and replacement with a new lens subjects the patient to further risk to vision and health which may be viewed as unacceptable to both the health care professional and the patient.
Thus, there is a need for an apparatus and method for testing the ability of a subject to see properly using a bifocal IOL. In addition, there is a need for an apparatus and method to compare a subject's vision through different types of IOLs. Another need in the vision care community is an apparatus and method to monitor over months or years the geometrical and refractive configuration of an eye. The apparatus and methods of the current invention address these needs.